U.S. Pat. No. 5,253,911 A discloses a controlled gripper wherein at its holder of two gripper claws, an electric servomotor is mounted which symmetrically swivels, via a rotary cam, the gripper claws in the closing direction against the force of an opening spring. The gripper claws not only symmetrically move in opposite directions, but compulsorily assume exactly predetermined relative positions at the holder in the gripping position and in the release position. These relative positions very precisely determine the position of the gripped object and the gripping and deposit points with respect to the holder. These relative positions are invariable.
WO 98/22374 A discloses a controlled gripper whose two gripper claws are actuated in parallel and symmetrically with respect to each other in opposite directions each linearly by an electric servomotor mounted at the holder. The gripping position and the release position, or the gripping and deposit points, respectively, have exactly predetermined relative positions relative to the holder which are invariable.
Gripper claws of such controlled grippers actuated by electric servomotors offer the advantage of a sensitive control and the elimination of mechanically complicated curved path controls which require lubrication and are therefore not hygienic and occupy much space, as they have for decades become the standard for controlled grippers in container treatment machines.
WO 2009/144664 A discloses an uncontrolled gripper where mechanical or magnetic energy storage mechanisms symmetrically act on its gripper claws, for example in the closing direction, and where the gripper claws are forced apart in the opening direction by the preform or container during acceptance or delivery. Such uncontrolled mechanical grippers generate high closing forces in the gripping position which can generate, for example at heated preforms, deformations or, in the acceptance or delivery of containers, undesired frictional forces. An electric servomotor, which acts at an arm supporting the holder of the gripper, swivels the gripper relative to the center of rotation of a starwheel defining the transport section, for example to compensate a pitch distortion or to change the relative distances between successive preforms or containers. The servomotor does not have any influence on the gripper claw movements.
Among other things, it is the job of the gripper in a container treatment machine or in a transport section between container treatment machines in a container treatment plant to transport the preform or container, to accept it from a transport section or station of a container treatment machine at an exactly predetermined position, and to deliver it to another transport section or station of a container treatment machine at an exactly predetermined position. For this, controlled or uncontrolled grippers with two or more than two gripper claws are common. Controlled grippers are actuated into the opening and/or closing direction, while uncontrolled grippers have a mechanically defined gripping position to which the gripper claws are pretensioned, for example by an energy storage mechanism, such as a spring, or by magnets. In the acceptance or delivery, the gripper claws of an uncontrolled gripper are opened with a relative motion of the preform or container against the force of an energy storage mechanism, whereupon they are moved towards each other again by the energy storage mechanism.
In procedures in container treatment plants or in container treatment machines, however, different problems arise in practice which result, among other things, from the functional principle of the grippers, wear, work tolerances and a susceptibility of the treated preforms or containers to mechanical loads generated by the grippers.
For example, the gripper accompanies, in the delivery of a preform into the blow mold of a blow molding station, the blow mold along a portion of its, for example, circular path about the machine's axis. With high machine performances, for example, of a rotary machine (up to 72000 containers/h), the gripper follows the blow mold, by means of overlaid swiveling and linear motions of a controlled transfer arm, simultaneously aligning the center of the preform with the center of the blow mold until the blow mold is closed. With an uncontrolled gripper, the closed blow mold in which the preform is seized pulls the preform out of the gripper. This drawing off, however, results in a shaking displacement of the preform in the blow mold. This fault can be reduced by using a controlled gripper (active opening, spring-loaded closing). Nevertheless, an oscillating motion of the preform often occurs due to which the preform is no longer positioned sufficiently exactly relative to the blow mold halves. The preform is then touched first by one of the halves of the closing blow mold and displaced. This disadvantageous effect is even amplified by the small difference in the diameter in the holding region of the blow mold compared to the diameter of the preform. Due to a displacement of the preform in the blow mold in such a disharmonic delivery from the gripper, the stretching rod inserted into the blow mold does no longer hit the center of the preform's bottom dome as actually predetermined. A so-called off-center effect occurs where the injection point or pressure point of the preform usually located in the center of the container's bottom is displaced to the outside to container bases. This results in an unstable container bottom as the wall thickness is thicker on one side than on the side of the bottle bottom where the stretching rod contacted the preform eccentrically. The deposit point is adjusted by the operator as precisely as possible via adjusting facilities at the gripper, at the starwheel or at the blow mold during the installation. However, it regularly occurs that the maintenance intervals for precise recalibration are not respected. Such recalibration optionally also becomes necessary when the machine performance is increased or reduced because this, too, can result in a displacement of the deposit point adjusted during the installation.
In the preferential heating of preforms, each preform is introduced, at a holding arbor or an internal gripper, into an intermediate module after a heat treatment uniform in the circumferential direction, where in the intermediate module, discrete regions, e.g. of the side wall, are touched by at least two e.g. shell-like contact elements to apply a temperature profile varying in the circumferential direction (e.g. by heat abstraction) before the preform is blow molded. This is suitable, for example, for the manufacture of a noncircular or oval container which is to obtain identical and/or different wall thicknesses both in regions more strongly stretched in the circumferential direction as well as in regions less strongly stretched in the circumferential direction. Depending on the procedure, the preform is squeezed by the contact elements to an extent that cannot be adjusted to date because the contact elements then acting as gripper claws of a multifunctional gripper (e.g. transport function, positioning function, squeezing function, temperature controlling function), always grip the preform in the same manner e.g. via cam controls. In case of a change of types, at least the contact elements must be exchanged to date, which is very time-consuming.
Furthermore, differently dimensioned preform or container types require different gripping forces in the acceptance, delivery and during transport, while conventional grippers do not permit a force control or path control of the gripper claws to date.
In a blow molding station of a stretch-blow molding machine, the stretching rod drive sometimes fails, so that the stretching rod is not properly retracted from the blow mold after a blow-molding process when a new preform reaches the empty blow mold. Since conventional grippers operate with a compulsory and invariable motion sequence, one cannot consider the dangerous situation in case of a failure of the stretching rod drive, so that a collision between the preform held by the gripper and the stretching rod occurs, resulting in a malfunction. This also applies to other incorrect positions of parts of a blow molding station caused by a failure, such as the blow mouth, the mold locking, or the like.
In a container treatment machine, adjacent rotary machine sections, such as a blow-molding unit and a preform transfer starwheel, are adjusted to each other with a train of gears for a certain machine performance. During the installation, a misalignment of up to 0.3 mm is, for example, intentionally adjusted between the deposit point of the gripper and the center of the blow mold. With the determined machine performance, for example of 2000 containers/h, the operational load in normal operation then compensates the misalignment in the train of gears, for example of a belt connection, to zero, so that the preforms are exactly aligned with the center of the blow mold when they are deposited. If, however, the container treatment machine is operated at a lower machine performance, for example below 1000 containers/h, the operational load in the train of gears becomes lower, so that the adjusted alignment is then possibly no longer compensated and preform delivery problems occur if no corresponding previous change of the misalignment has been performed, which is time-consuming. To date, the grippers are not able to compensate this disadvantage without prior calibration works.
Grippers of a transport starwheel which accept preforms from holding arbors or internal grippers and transport them from the oven to the blow molding machine operate with a predetermined gripping power, although heavy or light preform types require different holding forces, as, for example, due to centrifugal force, heavy preforms have to be positioned more firmly than lighter preforms which naturally also have a less stable mouth or a slightly heated and therefore deformable thread. In case of a change of the preform type, therefore the gripping force would have to be correspondingly adapted, which is time-consuming and in many cases not possible as the gripping movement cannot be force-controlled and/or path-controlled.
In case of a temperature control of a preform in the oven, the preform is held with an internal gripper or a holding arbor from which the preform is taken, due to the geometry in the relative motions between the holding arbor and the transport starwheel, by the gripper of a transport starwheel forming a transport section which transports it to the blow molding machine. Preforms often have low threaded mouth regions at the mouth section, so that the holding arbor must immerge relatively deeply. Due to this, it can be located, during the acceptance, in the level of motion of the gripper claws of the accepting gripper. If now no preform is delivered by the holding arbor due to a malfunction, or if a defective preform has been discharged before, or if the machine is operated in the mode “only use every second pitch”, with conventional grippers, a collision between the gripper claws of an uncontrolled gripper and the holding arbor cannot be avoided because no preform is located in-between. This can lead to damages at the holding arbor and/or the gripper claws.
In a sterilizer or rinser, the gripper positions the preform or container with its mouth in alignment with an inlet nozzle for a sterilizing or rinsing agent which is introduced into the mouth under pressure obliquely or asymmetrically during a cycle. Here, the gripper can, during the cycle, even place the mouth rim of the mouth in positioning contact e.g. against at least one web holding the inlet nozzle. In order to be able to also treat the mouth rim and/or at least parts of the external thread of the mouth with the agent, a deflection bell can be placed above the inlet nozzle which deflects the agent exiting from the preform or container and applies it onto the mouth rim and/or externally onto the thread. A conventional gripper holds the preform or container during the complete cycle in an exactly predetermined position relative to the inlet nozzle which makes it difficult to intensify the treatment or to also properly treat the contact region between the mouth rim and the web and/or gripper claw contact regions. Here, at least an individual adjustability of the mouth relative to the inlet nozzle would be suitable, which, however, does not exist in conventional grippers. The procedure is similar in a rinser in the treatment with a rinsing agent. In particular, the gripper claws are swiveled in a plane which is perpendicular to the axis of the rinser or sterilizer jet. However, it would also be conceivable, as an alternative or in addition, to swivel the grippers such that the injection angle changes relative to the longitudinal axis of the containers to be treated. For this, an additional drive can also be provided. It would also be conceivable to measure the containers and/or their mouths before they enter the sterilizer with a sensor or a camera and to position the grippers on the basis of the measurement such that the jet of the sterilizer or rinser medium is individually adapted to each container. In particular, an optimal distance from the container mouth rim to the jet can be predetermined, either in percentages of the diameter or in millimeters from the rim. In containers with larger mouth diameters, the gripper claws would, after a central transfer, cover a further distance to the optimal position. As an alternative, the container could also be delivered to the gripper claws of the rinser or sterilizer eccentrically by this measure—i.e. already with the optimal distance to the nozzle.
Due to their curved path controls, conventional grippers often cause problems in the operation in a clean room environment, for example at transfer arms of transfer starwheels, as by wear and the required lubrication of the curved path controls, contamination of the clean room atmosphere can be hardly avoided, or as it is difficult to install clean room seal, which are technically extremely complicated. Here, grippers whose movements do not depend on a curved path control would have an essentially better clean room capability, paired with an individual actuation of the gripper claws which does not exist in conventional grippers at present.
In some container treatment plants, buffer transport sections or a so-called air transport device for carrying off containers are common. The containers are accelerated and transported inside them by air jets. In practice, however, problems can occur if a container handed over by a gripper of a transfer starwheel is not immediately properly accelerated and carried off by the air jets. Then, a jam of containers that can lead to container damages and requires the operator's intervention can occur. Conventional grippers completely disengage from the containers during transfer, so that it is up to the air transport device alone to properly accelerate the delivered container and to carry off containers at predetermined distances. A jammed delivered container can be even temporarily squeezed in the guidance of the air transport device by the following gripper claw of the gripper symmetrically set to the release position due to the bottom movement of the transfer starwheel because the gripper claw cannot be adjusted beyond the release position.